1. Field of the Invention
The present invention relates to a resist lower layer material of a multilayer resist film for use in microprocessing in the production process of semiconductor devices, and particularly to a resist lower layer material of a multilayer resist film suitable for exposure with a far ultraviolet ray, KrF excimer laser light (248 nm), ArF excimer laser light (193 nm), F2 laser light (157 nm), Kr2 laser light (146 nm), Ar2 laser light (126 nm) or the like. The present invention further relates to a method for forming a pattern on a substrate by lithography using the resist lower layer material.
2. Description of the Related Art
With the higher integration and higher operation speed of LSIs in recent years, demand is growing for finer pattern rules. However, lithography with optical exposure, the currently most commonly used technique, has almost reached the limit in terms of inherent resolution defined by the wavelength of light sources.
As the light source for lithography used when forming a resist pattern, exposure light using g-line (436 nm) or i-line (365 nm) of mercury lamps as a light source is widely used for the optical exposure, and as means for obtaining further finer patterns, the method of shortening the wavelength of exposure light has been considered effective. For this reason, in the mass production process for 64 M bit DRAMs, for example, KrF excimer laser (248 nm) having a short wavelength is employed as the exposure light source instead of i-line (365 nm). However, the production of DRAMs having an integration degree of 1 G or more, which requires a further finer microfabrication technique (e.g., processing size: 0.13 μm or less), requires the use of a light source having a shorter wavelength, and particularly a lithography that employs ArF excimer laser (193 nm) is under development.
A multilayer resist process such as two-layer resist process is conventionally known as being excellent in forming a pattern having a high aspect ratio on a stepped substrate. In order to develop a two-layer resist film with a commonly available alkaline developer in two-layer resist process, it is considered preferable to use a high molecular weight silicone compound having a hydrophilic group such as a hydroxy group or carboxyl group for forming a resist upper layer.
In relation to the high molecular weight silicone compound, chemically amplified silicone-based positive resist materials are proposed for KrF excimer laser which comprises a base polymer and an acid generator, the base polymer comprising polyhydroxybenzylsilsesquioxane, a stable alkali soluble silicone polymer, whose phenolic hydroxyl group is partially protected by a t-Boc group (see, for example, Japanese Patent Application Unexamined Publication 6-118651/1994 and SPIE vol. 1925 (1993) p 377). For ArF excimer laser, a positive resist comprising as a base polymer silsesquioxane in which cyclohexyl carboxylic acid is substituted by an acid-labile group is proposed (see, for example, Japanese Patent Application Unexamined Publication No. 10-324748/1998, Japanese Patent Application Unexamined Publication No. 11-302382/1999 and SPIE vol. 3333 (1998) p 62). For F2 laser, a positive resist comprising as a base polymer silsesquioxane having hexafluoroisopropanol as a soluble group is proposed (see, for example, Japanese Patent Application Unexamined Publication No. 2002-55456). These polymers contain polysilsesquioxane containing a ladder frame by polycondensation of trialkoxysilane or a trihalogenated silane in the main chain.
As the high molecular weight silicone compound in which silicon is suspended from a side chain, silicon-containing (meta) acrylic ester-based polymer is proposed (see, for example, Japanese Patent Application Unexamined Publication No. 9-110938/1997, and J. Photopolymer Sci. and Technol. Vol. 9 No. 3 (1996) pp 435 to 446)
The resist lower layer material for use in two-layer resist process can comprise, for example, a hydrocarbon compound that can be etched with an oxygen gas, or the like. Because the resist lower layer serves as a mask when the substrate under the resist lower layer is etched, it is preferable that the resist lower layer has a high etching resistance when the substrate is etched. When the resist lower layer is etched with an oxygen gas using the resist upper layer as a mask, the resist lower layer may be preferably composed only of a hydrocarbon containing no silicon atom. In order to improve the line width controllability of the resist upper layer containing a silicon atom, to suppress the unevenness of the sidewall of a pattern and the collapse of the pattern due to a stationary wave it is preferable that the resist lower layer has also a function of serving as an anti-reflection film. Specifically, it is preferable that the reflectivity from the lower layer into the resist upper layer is kept at 1% or less.
Meanwhile, proposed is a process for three-layer resist wherein a resist upper layer of a monolayer resist containing no silicon, a resist intermediate layer containing silicon, and a resist lower layer of an organic film are laminated in this order (see, for example, J. Vac. Sci. Technol., 16(6), November/December 1979).
Generally speaking, a monolayer resist containing no silicon is more excellent in resolution than a silicon-containing resist, and thus a high resolution monolayer resist can be used as an exposed imaging layer in three-layer resist process.
As the resist intermediate layer, a spin-on-glass (SOG) film is used, and many SOG films are proposed.
In three-layer resist process, the optimal optical constant of resist lower layer for suppressing the reflection of substrate is different from that in two-layer resist process.
Both two-layer resist process and three-layer resist process have the same purpose of suppressing the reflection of substrate as much as possible, specifically, down to 1% or less. However, in two-layer resist process, the anti-reflection effect is imparted only to the resist lower layer, whereas in three-layer resist process, the anti-reflection effect can be imparted to either or both of the resist intermediate layer and the resist lower layer.
Silicon-containing layer materials having an anti-reflection effect imparted thereto are proposed in, for example, U.S. Pat. Nos. 6,506,497 and 6,420,088, and the like.
It is widely known that a multilayer anti-reflection film has a greater anti-reflection effect than a monolayer anti-reflection film, and thus the multilayer anti-reflection film is widely used in industrial applications such as optical components and eyeglasses.
By imparting an anti-reflection effect to both the silicon-containing resist intermediate layer and the resist lower layer, a high anti-reflection effect can be obtained.
As for the resist lower layer for use in three-layer resist process, the resist lower layer is required to have, in addition to the effect as an anti-reflection film, a high etching resistance in the processing of the substrate.
For this reason, it is preferable to use a polymer having a high etching resistance and a higher carbon atom content and containing many aromatic groups for a lower layer for use in three-layer process.
Under the circumstances, a low dielectric insulating film has been used recently as the treatment layer of a substrate. As a low dielectric insulating film for achieving a dielectric constant of 2.5 or less, porous silica having a dielectric constant of 1 has been under study.
However, when a porous silica-based low dielectric insulating film is used, a problem arises that trailing skirts (poisoning) occurs in the positive resist after development. The cause for this is presumed to be that an amine substance is adsorped to the pores, and during a resist patterning process, particularly during baking, the amine substance is liberated from the pores through the resist lower layer to undergo a neutralization reaction with the acid comprised by the upper layer resist, causing the trailing skirts (see, for example, J. Photopolymer Sci. and Technol. Vol. 16 No. 3 (2003) pp 351 to 361). Therefore, development is desired for a resist lower layer that can reduce a harmful effect such as the trailing skirts of the upper layer resist caused by the amine substance.
As methods for preventing poisoning, a lower layer that can generate a sulfonic acid residue group by the application of heat or the like (see, for example, Japanese Patent Application Unexamined Publication Nos. 2004-177666 and JP 2004-179393), and a lower layer to which an amine salt of high molecular weight fluorosulfonic acid has been added (see, for example, Japanese Patent Application No. 2005-120636) are proposed. The lower layer to which a polymer having an acid group has been added is free from the evaporation of acid by baking, but because the acid group is immobilized, there is a disadvantage of low capability of neutralizing the basic substance generated from the substrate that can cause poisoning.
The method for improving the resist pattern by the addition of an acid or acid generator to the lower layer is conventionally known, and an intermediate film for three-layer resist process in which an ammonium salt that can generate antimonate has been added to a silicone resin (see, for example, Japanese Patent Application Unexamined Publication No. 5-267158/1993), an intermediate film for three-layer resist process in which an acid generator has been added (see, for example, Japanese Patent Application Unexamined Publication No. 5-291130/1993) and the like are proposed.
In the case where an acid generator is added, if the generated acid remains in the film, the anti-poisoning capability is high, but a problem arises that the anti-poisoning capability is reduced by the evaporation of acid during baking for cross-linking. Perfluorosulfonic acid, which is a super acid, is expected to exhibit a high anti-poisoning effect, but due to its low boiling point, perfluorosulfonic acid evaporates during baking, deteriorating the anti-poisoning effect. An alkylsulfonic acid such as camphorsulfonic acid has a high boiling point, but is weakly acid, and thus an alkylsulfonic acid has a low capability of trapping amine. An inorganic acid such as antimonite has a high boiling point and is a strong acid, but metal acids cannot be used for semiconductor applications. An ammonium salt has a thermal decomposition temperature lower than those of onium salts such as iodonium salt and sulfonium salt, and thus an ammonium salt can generate an acid by baking at a low temperature and can cure the film. A decrease of baking temperature prevents the evaporation of acid, leading to an improvement of anti-poisoning effect.
In this connection, there is disclosed a lower layer in which an acid generator of ammonium salt of toluene sulfonic acid has been added (see, for example, Japanese Patent Application Unexamined Publication Nos. 2003-114533 and 2005-331951), nonafluorobutane sulfonate triethylamine salt (see, for example, the specification of Japanese Patent Application Unexamined Publication No. 2002-372829), and nonafluorobutane sulfonate tripropyl amine salt (see, for example, Example of Japanese Patent Application Unexamined Publication No. 2004-28506). Also, a sulfonium salt and an iodonium salt that generate α-difluorosulfonic acid (Japanese Patent Application Unexamined Publication No. 2004-531749), and a sulfonium salt and an iodonium salt that generate α,β-tetrafluorosulfonic acid (Japanese Patent Application Unexamined Publication No. 2004-2252) are proposed.
In order to enhance the poisoning resistance, development of an intermediate layer and a lower layer in which an ammonium salt that can generate a super acid having a high boiling point has been added has been awaited.